With the continuous increase of optical transmission rate, signal coding technology is updated accordingly. At present, in 40G and 100G optical transmissions, a differential coding technology is mostly used, where it is required that pre-demodulation of a light phase and then optical-electrical conversion is performed at a receiving end to receive a signal. An optical demodulator implements the function of pre-demodulation of a light phase.
A current demodulator uses a waveguide technology, where the waveguide technology includes allocating light energy by using waveguide fabrication, and then adjusting one arm, so as to produce interference when two arms are coupled again, thereby implementing a function such as phase separation, as shown in FIG. 1.
The achievement of light splitting and interference by using a method of changing voltage to vary a waveguide refractive index requires a sufficient optical path to meet the requirements of phase adjustment. In this way, the waveguide needs to have a large area, and the demodulator needs to have a large volume accordingly.